Info Catalog elisp: Buttons elisp: Display elisp: Blinking

elisp: Abstract Display

 
 37.20 Abstract Display
 ======================
 
 The Ewoc package constructs buffer text that represents a structure of
 Lisp objects, and updates the text to follow changes in that structure.
 This is like the “view” component in the “model–view–controller” design
 paradigm.  Ewoc means “Emacs’s Widget for Object Collections”.
 
    An “ewoc” is a structure that organizes information required to
 construct buffer text that represents certain Lisp data.  The buffer
 text of the ewoc has three parts, in order: first, fixed “header” text;
 next, textual descriptions of a series of data elements (Lisp objects
 that you specify); and last, fixed “footer” text.  Specifically, an ewoc
 contains information on:
 
    • The buffer which its text is generated in.
 
    • The text’s start position in the buffer.
 
    • The header and footer strings.
 
    • A doubly-linked chain of “nodes”, each of which contains:
 
         • A “data element”, a single Lisp object.
 
         • Links to the preceding and following nodes in the chain.
 
    • A “pretty-printer” function which is responsible for inserting the
      textual representation of a data element value into the current
      buffer.
 
    Typically, you define an ewoc with ‘ewoc-create’, and then pass the
 resulting ewoc structure to other functions in the Ewoc package to build
 nodes within it, and display it in the buffer.  Once it is displayed in
 the buffer, other functions determine the correspondence between buffer
 positions and nodes, move point from one node’s textual representation
 to another, and so forth.  Abstract Display Functions.
 
    A node “encapsulates” a data element much the way a variable holds a
 value.  Normally, encapsulation occurs as a part of adding a node to the
 ewoc.  You can retrieve the data element value and place a new value in
 its place, like so:
 
      (ewoc-data NODE)
      ⇒ value
 
      (ewoc-set-data NODE NEW-VALUE)
      ⇒ NEW-VALUE
 
 You can also use, as the data element value, a Lisp object (list or
 vector) that is a container for the real value, or an index into some
 other structure.  The example (Abstract Display Example) uses
 the latter approach.
 
    When the data changes, you will want to update the text in the
 buffer.  You can update all nodes by calling ‘ewoc-refresh’, or just
 specific nodes using ‘ewoc-invalidate’, or all nodes satisfying a
 predicate using ‘ewoc-map’.  Alternatively, you can delete invalid nodes
 using ‘ewoc-delete’ or ‘ewoc-filter’, and add new nodes in their place.
 Deleting a node from an ewoc deletes its associated textual description
 from buffer, as well.
 

Menu

 
· Abstract Display Functions  Functions in the Ewoc package.
· Abstract Display Example    Example of using Ewoc.
 

Info Catalog elisp: Buttons elisp: Display elisp: Blinking